The fluid-mosaic model articulated by Singer and Nicholson provides a unifying hypothesis for the structure of biological membranes. A crucial aspect of this hypothesis is the interaction between proteins and lipids, but for nearly every case relatively little is known about such interactions. The coat protein (B-protein) from the filamentous phages (fd, M-13, fl, etc.) can be isolated in pure form in abundance, is extraordinarily hydrophobic, has a known sequence of just 50 amino acids, and forms tight associations with purified lipids. We (Dunker and Williams, J. Biol. Chem., 252, 6253, 1977) and others have shown that the B-protein can assume two distinct conformational states when associated with lipid. This is the only well-characterized example in which a protein in two distinct conformations associates with lipid. The core of this grant application is to compare with protein/lipid interactions of the two conformationally different protein states using laser Raman spectroscopy, differential scanning calorimetry, and electron microscopy. We have already carried out studies of the beta-sheet-rich, c-state B-protein complexed with dipalmatoyl lecithin using laser Raman spectroscopy. In this grant application we seek support to extend these studies to other lipids with differing head and tail groups and to repeat all of these studies with the B-protein in the vastly different, alpha-helix-rich b-state.